1. Field of the Invention
This invention relates to a double row thrust roller bearing in which a pair of inner and outer cages are arranged radially in two rows in separate coaxial relation, and each cage has a plurality of rollers rotatably held and retained respectively in pockets thereof.
2. Related Art
A double row thrust roller bearing of the type described is disclosed in JP-A-2007-224978 which was filed in Japanese Patent Office earlier by the present inventor. As shown in FIGS. 4 and 5, this double row thrust roller bearing includes a pair of inner and outer cages 20 and 120 arranged radially in two rows in separate coaxial relation. The radially-inner cage 20 includes an annular inner peripheral wall 41, an annular outer peripheral wall 51, and a plurality of pillar portions 30 interconnecting the inner and outer peripheral walls 41 and 51 at intervals in a circumferential direction of the inner and outer peripheral walls 41 and 51 such that the inner cage 20 has a generally M-shaped cross-section. The inner cage 20 has a plurality of pockets 31 each formed between the adjacent pillar portions 30. A retaining projection 33a is formed on a radially-intermediate portion of each of opposed edges 33 of the adjacent pillar portions 30, and projects into the pocket 31, and also retaining projections 33b are formed respectively on radially-opposite end portions of each edge 33, and project into the pocket 31. The radially-outer cage 120 is similar in construction to the inner cage 20. More specifically, the outer cage 120 includes an annular inner peripheral wall 141, an annular outer peripheral wall 151, and a plurality of pillar portions 130 interconnecting the inner and outer peripheral walls 141 and 151 at intervals in a circumferential direction of the inner and outer peripheral walls 141 and 151 such that the outer cage 120 has a generally M-shaped cross-section. The outer cage 120 has a plurality of pockets 131 each formed between the adjacent pillar portions 130. A retaining projection 133a is formed on a radially-intermediate portion of each of opposed edges 133 of the adjacent pillar portions 130, and projects into the pocket 131, and also retaining projections 133b are formed respectively on radially-opposite end portions of each edge 133, and project into the pocket 131. This double row thrust roller bearing comprises a pair of races 60 and 70, a plurality of (i.e., two rows of) rollers 10 interposed between the pair of races 60 and 70, and the two rows of cages 20 and 120 holding the two rows of rollers 10, respectively, such that rollers 10 of each row are disposed at predetermined intervals in the circumferential direction.
A prior technique relating to double row thrust roller bearings of the type described is disclosed, for example, in JP-A-2006-194292.
However, in the above double row thrust roller bearing, an inner peripheral surface of the annular inner peripheral wall 41 of the inner cage 20 is guided by an annular flange 61 formed at an inner peripheral edge of the race 60 as shown in FIG. 5. Also, an outer peripheral surface of the annular outer peripheral wall 151 of the outer cage 120 is guided by an annular flange 71 formed at an outer peripheral edge of the other race 70. Therefore, a large clearance C develops between the annular outer peripheral wall 51 of the inner cage 20 and the annular inner peripheral wall 141 of the outer cage 120, and as a result when the two cages were thus provided in a double-row manner, there was encountered a problem that the dimension of the roller bearing in the radial direction was increased.